Viscous Effects on Performance of Two-Dimensional Supersonic Linear Micronozzles

A comprehensive numerical investigation of a steady viscous flow through a two-dimensional supersonic linear micronozzle has been performed. The baseline model for the study is derived from the NASAGoddard Space Flight Center microelectromechanical systems-based hydrogen peroxide prototype microthruster. On the microscale, substantial viscous subsonic layers may form on the nozzle expander walls, which reduce thrust and efficiency. One approach to compensate for the presence of these layers has been to designmicronozzleswith expansion angles larger than traditional macroscale nozzles. Numerical simulations have been conducted for a range of Reynolds numbers (Re 15–800) and for expander half-angles of 10–50 deg. Twodifferentmonopropellant fuels have been considered: decomposed 85% pure hydrogen peroxide and decomposed hydrazine. It is found that an inherent tradeoff exists between the viscous losses and the losses resulting from the nonaxial exit flow at larger expansion angles. Our simulations indicate that themaximumnozzle efficiency occurs for bothmonopropellants at a nozzle expansion halfangle of approximately 30 deg, which is significantly larger than that of traditional conical nozzle designs.